A dewar flask is a vessel for storing hot or cold liquids so that the liquids maintain their temperature independent of the surroundings. Typically, the walls of the dewar flask include two thin layers separated by a vacuum to reduce conduction and convection.
In one application, the dewar flask is used to store liquids, such as, liquid nitrogen, for use in various chemical processes. A dewar head assembly is often used to remove liquid from the dewar flask. The dewar head assembly typically includes a long pipe that extends through an opening at the top of the dewar flask. The dewar head assembly also typically includes a mechanism for controllably removing the chemical from the dewar flask through the pipe.
When used in a chemical process, the liquid in the dewar flask occasionally becomes depleted and must be replenished. During conventional refilling of the flask the dewar head assembly is removed from the dewar flask. Unfortunately, the character of liquids, such as nitrogen is such that the extreme cold of the dewar flask causes condensation to form on the dewar head assembly when removed from the dewar flask introducing environmental contamination, namely water to drip into the dewar flask. Introduction of water into the dewar flask may cause long term problems to equipment associated with the dewar flask. Also, this introduction of contaminants into the dewar flask may also affect the reliability of the equipment associated with the dewar flask. In an attempt to minimize this contamination, a procedure of towel drying, hot air drying and dry nitrogen drying of the pipe of the dewar head assembly is typically used. Unfortunately, the time to conduct this procedure is on the order of 30 minutes for each refill of the dewar flask.
The procedure of reinsertion of the dewar head after the dewar flask is refilled is also affected by the measures used to protect the contents of the dewar flask from contamination. Insertion of a dewar head assembly normally takes about 5 minutes. A much longer period of time is required after the drying of the pipe of the dewar head assembly because the dewar head assembly is warm compared to the liquid nitrogen. When the dewar head assembly is warm, the liquid nitrogen tends to splash on the person inserting the dewar head assembly if inserted too quickly and thereby raising a safety issue. Thus, the dewar head assembly is typically inserted slowly. This also raises a health/disability issue for the operator as a result of holding the dewar head assembly for an extended period of time.
Therefore, there is a need in the art for an improved technique for dispensing liquid into a dewar flask.